"Have you received the invitation letter for your family to visit the USA?"
If you received an invitation to the wedding then you do not need to bring the invitation to prove you were invited. If you never received an invitation to the wedding then it is not etiquette to attend the wedding and you would be considered crashing the wedding.
Invitation to the Wedding - 1983 is rated/received certificates of: Iceland:L
The Invitation - 2003 is rated/received certificates of: Australia:MA (2009) USA:R
Death by Invitation - 1971 is rated/received certificates of: USA:R
Invitation au voyage - 1982 is rated/received certificates of: USA:R
Invitation to Monte Carlo - 1959 is rated/received certificates of: UK:U
Answer You could always ask the person in question to confirm that indeed they received the email or if in the case that you received the invitation by email you could aways write them back notifying them that you received their email
Murder by Invitation - 1941 is rated/received certificates of: USA:Approved USA:Passed (National Board of Review)
Invitation to Hell - 1984 is rated/received certificates of: Finland:K-14 Germany:16 UK:15
Invitation to the Dance - 1956 is rated/received certificates of: Finland:S Sweden:Btl West Germany:12 (nf)
From their website:"Spotify free is currently in an invitation-only beta, which means you need to have received an invitation token to access the service."